Fuel metering system for an air valve carburetor



July 16, 1968 R. s. HARRISON FUEL METERING SYSTEM FOR AN AIR VALVE CARBURETOR Filed Feb. 13, 1967 2 Shets-Sheet l FIG].

F'IG.2

ATTORNEYS July 16, 1968 R. s. HARRISON 3,392,965

FUEL METERING SYSTEM FOR AN AIR VALVE CARBURETOR Filed Feb. 15, 1967 2 Sheets-Sheet 2 F'IG.3

F l G. 4

72 /lo 7" A5 INVENTOR ATTORNEYS United States Patent O 3,392,965 FUEL METERHNG SYSTEM FOR AN AIR VALVE CARBURETOR Robert S. Harrison, Detroit, Mich, assignor to Ford Motor Company, Dearborn, Mich, a corporation of Delaware Filed Feb. 13, 1967, Ser. No. 615,522 9 Claims. (Cl. 26139) ABSTRACT OF THE DISCLOSURE This fuel metering system comprises a ramp member positioned at one end by a temperature responsive element and at the other by a piston responsive to manifold vacuum. A lever connects the air valve with a fuel metering rod and rides on the ramp member so the relationship between the air valve and the fuel metering rod is determined by the position of the ramp member, which in turn is determined by the temperature and manifold vacuum of the engine. The ramp surface contacting the lever is contoured to produce proper fuel-air ratios at normal engine loads and temperatures. Compensation for variations in engine loads is provided by calibrating the movement of a piston connected to the ramp member in response to changes in manifold vacuum, and compensation for variations in temperature is provided by a cam connected to a temperature responsive element and acting on a lower surface of the ramp member. This lower surface also can be contoured to provide appropriate compensation.

Summary of the invention In some prior art fuel metering systems for air valve carburetors, the metering rod rides in the opening formed by overlapping slotted ar-ms. One of the slotted arms is moved by a temperature responsive element and a piston responsive to manifold vacuum while the other is moved by the air valve. Movement of the air valve is modulated by engine temperature and manifold vacuum to position the metering rod properly.

Other prior art systems use a metering rod that rides on a tapered cone movable laterally by the air valve and rotatably by devices responsive to temperature and manifold vacuum. Not only do these prior art systems have high manufacturing and assembly costs, but the systems contain relatively large masses in the linkage between the air valve and the fuel valve that prevent prompt response because of inertia.

This invention provides a fuel metering system that is easier to manufacture and assemble than prior art systems. In addition, a link having a relatively low mass connects the air valve with the fuel metering rod so the response of the metering rod to rapid movements of the air valve is much faster and more accurate than prior art systems. Furthermore, calibration and adjustment are more straightforward in the system provided by this invention.

The typical air valve carburetor has a carburetor body with an induction passage and a fuel source therein, a throttle blade mounted in the induction passage, and an air valve mounted in the induction passage anterior to the throttle blade. In such a carburetor, the fuel metering system provided by this invention comprises a fuel conduit connecting the fuel source with the induction passage between the air valve and the throttle blade. A metering valve controls the amount of fuel passing through the fuel conduit, and a lever connects the air valve with the metering valve. One end of the lever rides on a ramp ice member and the location of the lever on the ramp member determines the dynamic relationship between the air valve and the metering valve. The ramp member is contoured to provide the desired relationship between the air valve and the fuel valve at each opening of the air valve.

Fuel-air ratios are compensated for variations in engine temperature and operating load by using a thermally responsive means to position one end of the ramp member and a device responsive to manifold vacuum to position the other end. Engine temperature and operating load thus modulate the spatial location of any point on the surface of the ramp member, and the position of that point in turn determines the relationship between the air valve and the fuel valve, thereby establishing the fuel-air ratio that is proper for the engine under those conditions. The position of the ramp member can be tailored to the characteristics of the temperature responsive element by contouring the surface of the ramp member that contacts a cam connected to the temperature responsive element. This feature permits the use of standard temperature responsive elements.

Brief description of the drawings FIGURE 1 is a side sectional view of a carburetor containing the metering system of this invention showing the position of the air valve ramp member and lever when delivering idling fuel at low temperature. FIGURE 2 is a top view of the carburetor with a portion of the air valve and carburetor body broken away to show additional details of the metering system and the thermally responsive element. FIGURE 3 is a partial side View identical to FIGURE 1 except the carburetor is supplying fuel to a Warm engine at a partially open throttle blade setting; and FIGURE 4 is a partial side view identical to FIGURE 3 except the carburetor is supplying fuel to an engine accelerating at Wide open throttle through an intermediate speed.

Detailed description Referring to FIGURE 1, a carburetor body indicated generally by the numeral 10 comprises a main portion 12 with a cap portion 14 separated therefrom by a gasket 16. At the lower end of main portion 12 is a flange 18 adapted for fastening to the intake manifold (not shown) of an internal combustion engine by conventional means.

An induction passage 20 passes vertically through portions 12 and 14 to communicate with the atmosphere at the top of cap portion 14 and with passages in the intake manifold at the bottom of main portion 12. Adjacent induction passage 29 is a fuel bowl made up of a lower chamber 22 formed in main portion 12 and an upper chamber 24 formed in cap portion 14. Chambers 22 and 24 are separated by a portion of gasket 16 and communicate with each other only through a slot 26 formed in gasket 16.

Cap portion 14 contains a projection 28 extending into lower chamber 22, and a fuel inlet passage 30 is formed in cap portion 14 and projection 28. An inlet valve member 32 slides in the portion of inlet passage 30 formed in projection 28 to control the admission of liquid fuel into lower chamber 22. Valve member 32 is positioned in a conventional manner by a float (not shown). A tube 33 forming the fuel well projects downward from cap portion 14 into chamber 22 below the level of fuel therein.

A throttle blade shaft 34 is mounted in main portion 12 where it projects through induction passage 20. Fastened to shaft 34 Within induction passage 20 is a throttle blade 36. A throttle actuating lever 37 is fastened to shaft 34 outboard of carburetor body 10.

An air valve shaft 38 is mounted in cap portion 14 and has attached thereto an air valve 40. Air valve shaft 38 runs at right angles to throttle blade shaft 34, and air 3 valve 40 is anterior of throttle blade 36. Shaft 38 is cated at one side of induction passage 20. At the other side of induction passage 20 a boss 42 projects a short distance into pasage 20. Air valve 40 is bifurcated to pass around boss 42 when in its low air flow position.

A fuel conduit 44 formed in cap portion 14 and boss 42 opens at one end into induction passage 28 and communicates at the other with the top of the fuel well formed by tube 33. A thin metering jet 46 is positioned in conduit 44 where conduit 44 opens into induction passage 20. Passing vertically through boss 42 adjacent the opening of conduit 44 into induction passage 28 is an air dispersion hole 48. A fuel vapor hole 58 communicates at one end with upper chamber 24 and at the other with induction passage 20 just below the idling position of air valve 40.

Projecting from the underside of air valve 40 is a U- shaped member 52. A pin 54 passes through the downwardly extending legs of U-shaped member 52 parallel to air valve shaft 38 and a curved lever 56 is mounted pivotally at its center portion on pin 54. The end of lever 56 nearest boss 42 is connected to a fuel metering rod 58 while the other end projects into an enlarged cavity 68 formed in cap portion 14 and the upper part of body portion 12 on the side of induction passage 20 opposite chambers 24 and 22. Metering rod 58 has a tapered metering portion fitting slidably in metering jet 46 and extending into conduit 44.

At the lower outboard end of cavity 60, a hole 62 is bored into main portion 12. A passage 64 connects the lower end of hole 62 with induction passage 20 posterior of throttle blade 36. Slidably mounted in hole 62 is a pist-on 66 that is spring loaded by a spring 68 toward the upper end of hole 62. An arm 70 fastened to the top end of piston 66 projects upward into cavity 60 where it is fastened pivotally to one end of a ramp member 72. Arm 70 has a vertical slot therein and a top member 71 projects into the slot.

Ramp member 72 is positioned in cavity 60 so it extends in the same direction as lever 56. The inboard end of ramp member 72 rests on a cam 74 that is fastened securely to a rotatable shaft 76. Shaft 76 projects through main portion 12 substantially parallel to air valve shaft 38.

The end of lever 56 carries an adjusting screw 78, the tip of which rides on the upper surface 80 of ramp 72. A plug 82 is located in the top surface of cap portion 14 above adjusting screw 78.

Referring to FIGURE 2, a coil spring 84 is wound on pin 54 to urge lever 56 in a clockwise direction (as seen in FIGURE 1) so adjusting screw 78 stays in contact with surface 80. Air valve shaft 38 projects out of body 10 where it is fastened to a lever 86. An adjusting screw 88 threadably engages lever 86 and bears on a surface of cap portion 14. In addition, an air valve positioning spring 90 is fastened at one end to lever 86 and is anchored at the other end to cap portion 14.

Below and slightly outboard of shaft 38, shaft 76 projects into a housing 92 containing a thermally responsive bimetal element 94. An arm 96 connects thermally responsive element 94 with shaft 76. FIGURE 2 also shows that stop member 71 slides in vertical grooves formed in main portion 12 and is positioned by a set screw 98 threadably engaging a wall of main portion 12.

Operation Spring 90 acts through lever 86 to position air valve 40 so the vacuum or control signal existing between air valve 40 and throttle blade 36 is independent of the position of throttle blade 36 in accordance with conventional principles of air valve carburetors. Metering rod 58 cooperates wth metering jet 46 to control the amount of fuel supplied through fuel conduit 44, and lever 56 links movement of air valve 40 with metering rod 58 so metering rod 58 admits an increased amount of fuel when air valve 40 opens to admit increased amounts of air. The dynamic relationship between air valve 40 and metering rod 58 is determined by the position of the end of lever 56 that contains adjusting screw 78, which in turn is determined by the contour of surface 80. Surface of ramp member 72 therefore is contoured to produce a relationship that meters proper amounts of air and fuel for all openings of air valve 40.

An enriched fuel-air ratio is necessary when engine temperature is below normal. This enrichment is provided by the action of cam 74 on the lower surface of ramp member 72. At lower temperatures, temperature responsive element 94 acts through arm 96 to rotate shaft 76 in a counterclockwise direction in FIGURE 1. Cam 74 then engages the lower surface of ramp member 72 and moves the inboard end of ramp member 72 upward. This pivots lever 56 slightly counterclockwise which moves a smaller diameter of the tapered portion of metering rod 58 into a metering relationship with metering jet 46. Increased fuel then passes through fuel conduit 44 to enrich the fuel-air ratio. The position of the metering system when idling under this condition is shown in FIGURE 1.

As the engine warms, temperature responsive element 94 rotates shaft 76 in a clockwise direction so that cam 74 moves to the position shown in FIGURE 3. This permits the inboard end of ramp member 72 to move downward slightly, and spring 84 rotates lever 56 in a clockwise direction which decreases the amount of fuel supplied through fuel conduit 44. This reduces the fuel air ratio to the desired value. The position of the metering system when the engine is operating at a low speed under this condition is shown in FIGURE 3.

An increase in the fuel-air ratio also is required when accelerating the engine. When throttle blade 36 is opened to accelerate the engine, the manifold vacuum below throttle blade 36 decreases. The decreased vacuum is applied through passage 64 to the bottom of piston 66. Spring 68 then overcomes the force exerted by the manifold vacuum on piston 66 and moves piston 66, arm 70 and the outboard end of ramp 72 upward. Again, this rotates lever 56 slightly counterclockwise which in turn moves a smaller diameter of the tapered portion of metering rod 58 into a metering relationship with jet 46, thereby increasing the fuel-air ratio for acceleration. The position assumed by the metering system under this condition at normal temperature is shown in FIGURE 4.

Note that the enrichment provided by the temperature responsive element is more pronounced at low air valve openings and, hence, low engine speeds, while the enrichment provided by the decrease in manifold vacuum is more pronounced at higher air valve openings and higher engine speeds. These characteristics conform to basic engine requirements. In addition to contouring surface 80 of ramp member 72 to produce the desired fuel-air ratios, the surface of ramp member 72 contacted by cam 74 can be contoured to produce the desired response of ramp member 72 to the temperature responsive ele ment 94.

For idling, air valve 40 is opened slightly by adjusting screw 88 and idling fuel then is supplied through fuel conduit 44. Excess vapors from the fuel in lower chamber 22 pass into upper chamber 24 and are inducted through hole 50 into the engine while idling. As the engine assumes a road load, air valve 40 sweeps by the opening of hole 50 to stop the induction of fuel vapor through hole 50.

The basic position of lever 56 is adjusted relative to ramp member 72 by removing plug 82 and turning screw 78. Stop member 71 is used to adjust the maximum movement of piston 66. Conventional accelerating pump and cold starting enrichment mechanisms can be included in the carburetor of this invention if desired. Lever 56 is the only element connecting air valve 40 with fuel metering rod 58 and its mass is sufficiently low to reduce inertia to a very low value.

By pivoting the air valve at one side of the induction passage, improved metering accuracy is attained. Thus, this invention provides a fuel metering system for an air valve carburetor that is easily manufactured and assembled, has a low linkage inertia, and simplified calibration and adjustment. The cover over the lower chamber of the fuel bowl limits formation of fuel vapors and means are included in the carburetor for inducting excess fuel vapor into the engine while idling.

What is claimed is:

1. In an air valve carburetor having a carburetor body with an induction passage and a fuel source therein, a throttle blade mounted in said induction passage, and an air valve mounted in said induction passage anterior to said throttle blade, a fuel metering system comprising a fuel conduit connecting said fuel source with the induction passage between the air valve and the throttle blade,

metering means for controlling the amount of fuel passing through said fuel conduit,

a movable ramp member,

a thermally responsive means contacting one end of the ramp member and a manifold vacuum responsive means contacting the other end of the ramp member 'so said ramp member is positioned by a combination of these responsive means, and

a lever connecting said air valve with said metering means, said lever riding on said ramp member so the dynamic relationship between the air valve and the metering means is determined by the location of the lever on the ramp member.

2. The carburetor of claim 1 in which the metering means comprises a metering jet positioned in the fuel conduit near the opening thereof into the induction passage and a metering rod slidable in said jet, said rod being attached to said lever.

3. The carburetor of claim 2 in which the air valve is pivoted at the side of the induction passage.

4. The carburetor of claim 3 in which the air valve is connected to the central portion of said lever, the metering rod is connected to one end of the lever, and the other end of the lever rides on the ramp member.

5. The carburetor of claim 4 in which the thermally responsive means comprises a bimetal element connected to a shaft rotatably mounted in the carburetor body, said shaft having a cam contacting the underside of the inner end of the ramp member so rotation of said shaft by the bimetal element acts through the cam to position the ramp member.

6. The carburetor of claim 5 in which the manifold vacuum responsive means comprises a piston connected to the outer end of the ramp member, a spring urging said piston and said ramp member upward, and passage means subjecting the bottom of said piston to manifold vacuum.

7. The carburetor of claim 6 in which a stop member limits maximum movement of said piston.

8. The carburetor of claim 1 in which the thermally responsive means comprises a bimetal element connected to a shaft rotatably mounted in the carburetor body, said shaft having a cam contacting the underside of the inner end of the ramp member so rotation of said shaft by the bimetal element acts through the cam to position the ramp member.

9. The carburetor of claim 1 in which the manifold vacuum responsive means comprises a piston connected to the outer end of the ramp member, a spring urging said piston and said ramp member upward, and passage means subjecting the bottom of said piston to manifold vacuum.

References Cited UNITED STATES PATENTS 1,831,376 11/1931 Berry et al. 26150.1 1,855,383 4/1932 C-apell 26150.1 2,457,570 12/ 1948 Leibing 26l50 2,996,051 8/ 1961 Mick 261- 3,053,240 9/1962 Mick 26150 3,263,974 8/ 1966 Braun et a1. 26150 3,279,767 10/1966 Stoltman 26150.1 3,281,132 10/1966 Barnes 261-50.1 3,322,408 '5/1967 Stoltman 26150.1

HARRY B. THORNTON, Primary Examiner.

TIM R. MILES, Examiner. 

